1. Field of the Invention
The present invention relates to a releasable chucking device for a rotating medical or dental tool.
2. Description of the Related Art
A special type of medical or dental tools, which are operated with relatively high torques, have at the chucking end in the tool shaft a flattened portion for transmitting the torque. In addition, the tools have in the area of the flattened portion an annular groove, wherein a holding member of the chucking device protrudes radially inwardly into the annular groove during the operation of the tool in order to hold the tool in axial direction.
The circular cylindrical tool shaft is received in a circular cylindrical recess of the handpiece head with as little play as possible. This play usually is a few hundredth of a millimeter in the radial direction; this is due to the tolerances of the dimensions particularly of the tool shafts.
However, in a chucking device of the above-described type, even this little play has drastic effects on the operation of such tools because of the extremely small dimensions of the tool and, thus, of the tool head. This is because a play of a few hundredth of a millimeter means that the drill is movable in an order of magnitude which may correspond to half the chucking height. Particularly in view of the rates of rotation used in such tools, this means that the dimensional accuracy of the bore is significantly impaired, the quality of the bore surface and the bore edges is significantly reduced and vibrations and pain for the patient are increased.
Tool holders for such tool shafts are known, for example, from DE 30 12 240 A, DE 34 42 386 A, DE-G 89 13 626.8 U, EP 0 322 896 B, EP 0 470 324 B, and EP 0 820 734 A. All these known tool holders have the disadvantages described above.